Effect of three drying methods on the physicochemical composition of three varieties of onion (Allium cepa L).

The effect of solar and electric drying on physicochemical composition of onion (Allium cepa L) has been studied to reduce the post-harvest losses of onion bulbs. The physicochemical and biochemical composition of three varieties of onion (White of galmi, Violet of galmi and Goudami) were also investigated using the Fourier transform infrared (FT-IR) spectroscopy (4000-400 cm- 1) and scanning electron microscopy (SEM). Protein, sugar, lipid, moisture, ash, vitamin C, and color parameters were assayed on fresh and dried onion powders. The results showed that water was the main constituent of the fresh onion bulbs (87%). They were also rich in available sugars ranging from 19 g to 59 g/100 g and proteins 4 g to 11 g/100 g of dry matter (DM). Moreover, Ca, K, P, and Mg were found to be the major minerals of the onion powders. In general, the drying process influenced significantly (P<0.05) all the parameters, especially vitamin C that decreased considerably during the process with 90.55%, 78.71% and 72.50% for White of galmi, Goudami and Violet of galmi respectively. The FT-IR spectra showed major peaks were at the wavelength of 1024 cm-1. This could be due to vibrational frequency of ACH2OH groups of carbohydrates for the three studied varieties and for the two types of drying. Finally, a nonsignificant correlation was observed between drying methods and varieties of onion powders.